This invention relates to repeater stressing circuits and more particularly to circuits for remotely stressing digital radio repeaters independent of repeater spacing and received signal strength.
Digital radio systems generally require a plurality of regenerative repeaters along the transmission path to reconstruct the digital signal to overcome the degrading effects of noise and distortion. The distance between repeaters is chosen to maintain an adequate signal-to-noise ratio for essentially error free performance. As the signal-to-noise ratio decreases along the transmission path the error rate at the terminal end of the digital transmission path increases proportionately. It is therefore important to maintain an adequate signal-to-noise ratio at all points along the transmission path. A decrease in signal-to-noise ratio may be caused by, among other things, rain fade, transmitter power loss or by a failure in the regenerative repeater itself.
Testing of regenerative repeater performance in a digital radio system is an important aspect of transmission system maintenance. The numerous regenerative repeaters, however, are frequently positioned at locations which are difficult for a craftsman to reach for field testing. Field testing of repeater function is accordingly difficult, time consuming and expensive.
It is an object of the invention to enable all regenerative repeaters in a digital radio transmission system to be tested without the necessity of dispatching a craftsman to the field location of each repeater. Such test apparatus for each regenerative repeater must be capable of being remotely activated. In addition, inasmuch as atmospheric conditions tend to change the signal-to-noise ratio along a digital radio transmission path, the operation of such testing apparatus must be independent of received signal strength at any repeater and independent of repeater spacing.